Conventionally, spread-spectrum clocks have been used to reduce electromagnetic interference (EMI), which is an important issue in the system design of electronic devices and the like. A spread-spectrum clock for reducing EMI is produced by modulating a reference clock having a constant frequency.
For example, elements of a scanner or other image-reading device used to control the timing for reading an image are themselves controlled based on a clock signal. However, a problem with conventional image-reading devices is the generation of EMI when the various components are controlled based on the pulses of a reference clock having a constant frequency. Further, if the same components are controlled based on the pulses of a spread-spectrum clock obtained by frequency-modulating a reference clock on a time axis, the data acquisition timing may vary since the clock pulses are not constant.